Deflection system for flat cathode ray tube having canted electron gun in plane parallel to display screen



3,461,333 G CANTED S. E. HAVN Aug. 12. 1969 DEFLECTION SYSTEM FOR FLATCATHODE RAY TUBE HAVIN ELECTRON GUN IN PLANE PARALLEL TO DISPLAY SCREENOriginal Filed Sept. 29, 1961 5 Sheets-Sheetl FIG.I.

HIS ATTORNEY.

Aug. 12, 1969 s. E. HAVN 3,461,333 DEFLECTION SYSTEM FOR FLAT CATHODERAY TUBE HAVING CANTED ELECTRON GUN IN PLANE PARALLEL TO DISPLAY SCREENOriginal Filed Sept. 29, 1961 5 Sheets-Sheet 2 H62. FIG.3.

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INVENTORZ SVEND E. HAVN,

HIS ATTORNEY.

Aug. 12, 1969 s, v 3,461,333

DEFLECTION SYSTEM FOR FLAT CATHODE RAY TUBE HAVING CANTED ELECTRON GUNIN PLANE PARALLEL TO DISPLAY SCREEN 5 Sheets-Sheet 5 Original FiledSept. 29, 1961 use-- INVENTOR: SVEND E. HAVN,

BY M61622.

HIS ATTORNEY.

Aug. 12, 1969 E HAVN 3,461,333

s.. DEFLBCTION SYSTEM FOR FLAT CATHODE RAY TUBE HAVING CANTED ELECTRONGUN IN PLANE PARALLEL TO DISPLAY SCREEN 7 Original Filed Sept. 29, 19615 Sheets-Sheet 4 (x I 1 21s I PRIOR ART FIG.I2

I I l I I l I 222 i l I 217"? 1 i 1 l 1 l I I 22s 236 x I U L:. .J 22229 2 ..-217

PRIOR ART INVENTOR:

SVEND E. HAVN BY M Q 54%- H|$ ATTORNEY.

n t 3 w 1 m h 6 T w 4 N S IA 3 C a S. E. HAVN Aug. 12,1969

DEFLECTION SYSTEM FOR FLAT CATHODE RA ELECTRON GUN IN PLANE PARALLEL TODISPLAY SCREEN Original Flled Sept. 29, 1961 FIG.I3.

INVENTOR SVEND E. HAVN HIS ATTORNEY.

United States Patent U.S. Cl. 3l3-77 6 Claims ABSTRACT OF THE DISCLOSUREA cathode ray tube having improved means for producing, deflecting andfocusing an electron beam in a plane spaced from and generally parallelto the tubes image target plane. The image target has first and secondorthogonal scan dimensions and the beam produced originates at a pointthat is displaced from and travels in an initial path that is cantedrelative to both of these dimensions. First and second scanning meansare provided for respectively cyclically scanning the beam along the twoscan dimensions. The first scanning means includes both dynamic andstatic deflection means. The dynamic deflection means is disposed acrossthe initial path of the beam with its center of deflection displacedfrom both scan dimensions and dynamically deflects the beam along aplurality of angularly spaced diverging paths. The static deflectionmeans comprises means for producing a substantially unidirectionalmagnetic field across the diverging paths and performs the dual functionof statically deflecting the beam therefrom along a succession ofcollimated paths generally parallel to the second scan dimension andalso varying the focal length of the beam as it travels along difierentones of the collimated paths such that the focus of the beam focalpoints lies along a line generally parallel to the first scan dimension.The second scan means comprises dynamic deflection means disposed acrossthe collimated paths for dynamic-ally deflecting the beam therefromtoward the target area.

This is a continuation of application Ser. No. 141,863, filed Sept. 29,196 1.

This invention relates to cathode ray tubes, and more particularly tocathode ray tubes of the flat type having a relatively short distancebetween the front and back thereof. The invention primarily is concernedwith an arrangement for producing and deflecting an electron beam in aplane behind and generally parallel to the viewing screen of a flatcathode ray tube, in such a manner as to achieve good focusing and otherdesirable character'- istics of the electron beam at the viewing screen.

Various cathode ray tubes of the flat type which have been proposed inthe prior art are constructed to provide a horizontal deflecting meansfor cyclically scanning an electron beam in a first or horizontaldirection in a plane behind and parallel to a phosphor viewing screen,this electron beam extending in a generally vertical direction. Verticaldeflecting means are also provided for variably directing thehorizontally deflected electron beam frontwardly toward the screen in acyclical scanning manner in a second or vertical scanning direction.Present television scanning standards require a horizontal scanning rateof 15,750 cycles per second and a vertical scanning rate of 60 cyclesper second. These horizontal and vertical scansions of the electron beamdefine a raster on the viewing screen. The design and construction of aflat tube incur problems concerning electron beam focusing on thescreen, linearity, and other problems, as will be explained hereinafter.It is to be understood that the terms horizontal and vertical scanningare used in a relative sense, for convenience, to denote two mutuallyperpendicular directions of scanning at the Viewing screen, and thehorizontal scanning may in fact be vertical and the vertical scanningmay in fact be horizontal, or the tube may be turned on its side,without departing from the scope and meaning of the language usedherein.

An object of the present invention is to obviate *the aforementionedproblems of prior art flat cathode ray tubes.

Another object is to provide a flat cathode ray tube structure havingimproved performance and simplified construction.

An additional object is to provide improved arrangements for producingand deflecting an electron beam, and to provide such arrangementsrequiring only nominal amounts of electrical power.

A further object is to provide a flat cathode ray tube having improvedfocus of the electron beam at the viewing screen.

A still further object is to provide a flat cathode ray tube having asmall size and utilizing readily obtainable deflection signals.

Still other objects will be apparent from the following description andclaims, and from the drawing in which:

FIG. 1 is a front view of a cathode ray tube in accordance with thepresent invention;

FIG. 2 is a side view of the arrangement of FIG. 1, looking toward theleft side thereof;

FIG. 3 is a side view of the arrangement of FIG. 1, looking toward theright side thereof;

FIG. 4 is a perspective view of a portion of the embodiment of FIGS.1-3, shown partly broken away to reveal interior construction thereof;

FIG. 5 is a cross-sectional view of a portion of FIG. 1, taken on theline 5-5 thereof;

FIG. 6 is a cross-sectional view of a portion of FIG. 5, taken on theline 6-6 thereof, and showing details of an electron gun arrangement;

FIGS. 7-10 constitute a graphical explanation of the analyticalprocedure employed in the design of a cathode ray tube in accordancewith the invention;

FIGS. 11 and 12 illustrate focusing of the electron beam at the viewingscreen in some prior art types of cathode ray tubes;

FIG. 13 illustrates focusing of the electron beam at the viewing screenin a cathode ray tube in accordance with the present invention; and

FIG. 14 is a front view of a cathode ray tube in accordance with theinvention, illustrating a modified construction.

The invention comprises, in its basic preferred embodiment, a source ofa converging electron beam, and a lens arrangement for scanning the beamin a plane behind (or in front of) a viewing screen, the lensarrangement comprising a first deflection lens element in the path ofthe beam for variably deflecting the beam over an angle, and a seconddeflection lens element in the path of the beam as deflected by thefirst lens element, the second lens element comprising means forproducing a unidirectional field for deflecting the beam in a directionbehind (or in front of) the viewing screen, the lens arrangement havingrelatively different strengths of focus action on the convergingelectron beam at different regions of the deflected beam in order tocontrol the location of the cross-over point of the electron beam so asto provide focus of the beam at the screen. In accordance with apreferred embodiment of the invention, the center of deflection of theelectron beam as deflected by the first lens element is located belowand sideways from the viewing screen, and the aforesaid second lenselement is a unidirectional magnetic field having a tapered shape.

3 The invention further comprises specially shaped magnetic pole piecesfor producing the aforesaid magnetic field, whereby improved focus isachieved. The invention also comprises a specially shaped tube envelope,and other features that will become apparent, for achieving an irrvproved flat cathode ray tube.

The preferred embodiment of the invention, shown in FIGS. l-3 of thedrawing, comprises an evacuated envelope 46, preferably of glass, havinga front wall 47 and a back wall 48. These front and back walls may besubstantially mutually parallel, and the distance between themconstitutes the relatively shallow overall depth of the flat tube. Thefront wall 47 of the envelope 46 is recessed at the lower portion 49thereof, so that this portion of the tube has considerably lessdistance, preferably less than half the distance, between the front andback thereof than does the upper portion of the tube. A phosphor viewingscreen 50, or other suitable target for an electron beam, is positionedwithin the envelope 46 adjacent to or on the front wall 47. The envelope46 is provided with an inclined neck 51 extending from a corner of thelower portion 49 and generally in the plane thereof, as shown. A base52, attached to the neck 51, is provided with electrical connectorprongs 53. An electron gun 54 is provided within the neck 51 forprojecting an electron beam 55 generally parallel to and in the generaldirection of the phosphor screen 50.

A two-stage horizontal deflection arrangement, which constitutes a lensarrangement for the electron beam 55, comprises a first stage 56, whichconstitutes a lens element for the electron beam, having a yoke 57 ofmagnetic material, this yoke being generally U-shaped and provided witha pair of pole pieces 58, 59 at the ends thereof. The yoke 57 and polepieces 58, 59 may be constructed as an integral unit, or may be formedfrom separate pieces. A winding 61 is positioned around the yoke 57, anda source 62 of suitable horizontal deflection signals is connected toends of the winding 61 by means of connection wires 63, 64. The firststage of the horizontal deflection assembly is positioned with respectto the envelope 46, so that the pole pieces 58, 59 thereof are onopposite sides of the envelope 46 in the general vicinity of thejunction of the neck 51 and the remainder of the tube envelope, the polepiece 58 being in back of the envelope and the pole piece 59 being infront of the envelope, the entire first stage of the horizontal magneticdeflection system thus being located externally of the envelope 46.Preferably the envelope 46 is narrowed down at both the front and backthereof, as indicated at 66 and 67, so that the pole pieces 58, 59 willbe positioned as closely as is feasible to the electron beam 55.

A representative signal supplied by the deflection circuit 62 isindicated at 68 in the drawing. This deflection signal, when applied tothe winding 61, produces a cyclically changing magnetic field betweenthe pole pieces 58 and 59, which causes the electron beam 55 to scansequentially from a leftmost nearly vertical position 71 to a rightmostnearly horizontal position '72, the undeflected position of the electronbeam being approximately centrally located as indicated at 73. The polepieces 58, 59 may be suitably shaped to provide a desired degree oflinearity of the electron beam scansion with respect to time, inconjunction with the wave form of the horizontal deflection signal 68.

The second stage or lens element 81 of the two-stage horizontaldeflection arrangement comprises a pair of elongated suitably shapedpole pieces 82, 83 of magnetic material such as iron positionedgenerally mutually parallel to each other and extending generally acrossthe lower portion of the envelope 46 at the back 48 and front 49thereof, respectively, and tilted generally from upper left to lowerright, as shown. The pole pieces 82, 83 are tapered and the wide endsthereof extend beyond the right edge of the envelope 46, as shown, sothat a permanent magnet 84 may be positioned therebetween to provide amagnetic field in the space between the pole pieces 82 and 83. Amagnetic shunt member 85, made of magnetic material such as iron, isprovided across or between the pole pieces 82 and 83, and is rotatable,slideable, or otherwise positionable, to permit adjustment of thestrength of the magnetic field between the pole pieces 82 and 83.Alternatively, if desired, a winding may be placed around the magnet 84,or otherwise positioned with respect to the pole pieces 82, 83, and maybe connected to a source of adjustable current for adjusting themagnetic field strength. The entire sec ond-stage assembly 81 is locatedexternally of the envelope 46, as shown, and the magnetic field extendsbetween the pole pieces 82 and 83 transversely to the plane in which thebeam 55 is deflected by the first stage 56, whereby the electron beam 55passes through this field after being deflected by the first stage 56and before reaching the space behind the screen 50. The magnetic fieldbetween the pole pieces 82, 83 is unidirectional in magnetic polarityalong the entire length thereof. The pole pieces 82, 83 are long enoughso that the length of the magnetic field produced therebetween extendsacross the width of the screen 58 and across the entire space in whichthe electron beam 55 is usefully deflected by the horizontal deflectionpole pieces 58, 59 of the first stage 56, i.e. from the leftmost beamposition 71 to the rightmost beam position 72.

The second stage pole pieces 82 and 83 preferably are shaped as shown sothat the leading and trailing edges 91, 92. thereof are both concavetoward the approaching electron beam 55. However, other specific shapesof the pole pieces may be designed in accordance with the principles ofthe invention. These pole pieces 82, 83 are generally inclined fromupper left to lower right, as shown in the drawing, and are wider at therighthand end which is relatively farther from the electron gun 54 thanat the left-hand end thereof which is relatively nearer the electron gun54.

The leading and trailing edges 91, 92 are tapered with respect to eachother and this taper varies in a manner to achieve optimum focus as willbe described.

FIG. 1 shows a tube in accordance with the invention drawn to exact sizeon the patent drawing (reduced to about /3 actual size on patentcopies), with the second stage pole pieces 82, 83 shaped and orientedexactly in a manner found to produce satisfactory results. A way ofdesigning these pole pieces will be described subsequently.

The magnetic field produced between the pole pieces 82, 83 deflects theelectron beam 55 upwardly by varying predetermined amounts as a functionof horizontal position of the deflected electron beam, so that theelectron beam will always be vertically oriented when it leaves thismagnetic field. That is, the principal or central rays of the electronbeam will be vertical upon the beam leaving the magnetic field. Forexample, the vertical beam paths 93, 94, 95 are obtained, respectively,from the differently angled beam paths 71, 72, 73, because the beam whenin the nearly vertical path '71 passes through a narrower magnetic fieldand hence is deflected less than when passing through a greater width ofmagnetic field as in the nearly horizontal path 72. The amount ofdeflection of the electron beam by the magnetic field between the polepieces 82 and 83, may be affected by varying the magnetic fieldintensity along the length of the pole piece arrangement, as by varyingthe spacing between the pole pieces 82, 83 along their lengths. Towardthe right-hand end of the horizontal beam deflection, as in the beampath 72, there is a substantial horizontal component, as well as avertical component, of distance of beam travel in the magnetic field andhence the pole pieces need not be as wide at this region thereof aswould otherwise appear necessary for deflecting the beam to a verticaldirection. The beam, when in intermediate paths, is deflectedcorresponding intermediate amounts. There are numerous combinations ofshapes and positions of the magnetic field that will achieve theaforesaid vertical orientation of the electron beam.

After the horizontally scanned electron beam enters the region of thetube behind the viewing screen 50, vertically oriented as describedabove, it is controlled by a vertical deflection system which causes thebeam to be deflected toward the viewing screen 50 in a repetitivesequence whereupon the point of impingement of the beam on the screenmoves from top to bottom thereof in a cyclical manner. Variousarrangements are known for accomplishing the vertical deflection. Apreferred vertical deflection system is shown in FIGS. 4 and 5 of thedrawing, and is the subject matter of patent application Ser. No.141,862 filed Sept. 29, 1961 and now US. Patent No. 3,155,872 issuedNov. 3, 1964 to the present inventor and Harry T. Freestone and assignedto the same assignee as the present invention.

Now referring briefly to the vertical deflection arrangement shown inFIGS. 4 and 5, a plurality of electrical conductors 116 extendhorizontally in mutually parallel relationship and are positioned withinthe envelope 46 in a plane near or against the back 48 thereof. Theconductors 116 are electrically interconnected by a series arrangementof resistors 117 which may be in the form of a strip of resistivematerial painted or otherwise deposited along the inside of the envelope46 and against the conductors 116 a shown.

One or more elongated electrical conductors 118 are positionedhorizontally and mutually parallel within the envelope 46 against oradjacent to the top side 119 thereof. These conductors 118 areinterconnected by a series arrangement of resistors 121 which alsoconnect the array of conductors 118 serially to the array of conductors116. The resistors 121 may comprise a continuation of the strip ofresistive material which forms the resistors 117.

A layer 126 of electrically conductive material, such as aluminum, isdeposited or otherwise positioned against the back surface of thephosphor screen 50. The conductive layer 126 is electrically attached toa terminal pin 127 extending through the envelope 46, to which a sourceof positive direct potential, for example kilovolts, may be connected asindicated at 128. The front-most of the conductors 118 at the top of thetube is electrically connected to the conductive layer 126, eitherdirectly or via a resistance 121. The upper one of the conductors 116 iselectrically connected to a terminal pin 131 which extends through theenvelope 46 and to which may be connected a source of positive directpotential, for example 2 kilovolts, as indicated at 132. The lower oneof the conductors 116 is electrically connected to a terminal pin 133which extends through the envelope 46 and may be connected to a source134 of vertical deflection signals. A suitable vertical deflectionsignal, as produced by the source 134, and indicated at 135, may have,for example, a minimum value of about zero volts and a maximum value ofabout plus 8 kilovolts.

The values of the resistances 117 and 121 may be one megohm or greater.For example, these resistances may have equal values, or the valuesthereof may be graduated along the array of conductors, depending uponlinearity considerations of the vertical deflection system.

At the commencement of a vertical scansion, the vertical deflectionsignal 135 has a plus 8 kilovolts, whereupon the electron beam 55 willbe caused, by the electrostatic. field produced by the verticaldeflection array of conductors 116, 118 and 126, to assume a path asindicated by the numeral 136 in FIGS. 2 and 3 such that the electronbeam is deflected toward the viewing screen 50 and impinges thereon atthe upper part thereof. As the vertical deflection voltage 135 decreasesin value, the electrostatic field produced by the vertical scanningarray of conductors causes the electron beam 55 to deflect more sharplytoward the phosphor screen 50, as indicated by 6 the path 137 in FIGS. 2and 3. When the vertical deflection voltage 135 has a value of zero atthe end of a vertical scanning cycle, the electric field patternproduced by the array of conductors causes the electron beam 55 todeflect relatively sharply so as to impinge upon the phosphor screen 50at the lower part thereof, as indicated by the path 138 in FIGS. 2 and3.

When the electron beam 55 follows the path 136 under the influence ofthe vertical deflection arrangement and the path under. the influence ofthe horizontal deflection arrangement, it will impinge against thephosphor screen 50 at the point 141, as shown in FIG. 1. When theelectron beam 55 follows the path 137 under the influence of thevertical deflection arrangement and the path 93 under the influence ofthe horizontal deflection arrangement, it will impinge upon the screen50 at the point 142. Similarly, when the electron beam follows the path138 under the influence of the vertical deflection arrangement and thepath 94 as determined by the horizontal deflection arrangement, it willimpinge upon the screen 50 at a point 143. With a horizontal scanningrate at a higher repetitive frequency than the vertical scanning rate,as is conventional in television practice, the point of impingement ofthe electron beam 55 on the phosphor screen 50 will describe asuccessive series of horizontal lines in descending order, thus forminga raster on the area of the screen 50.

If desired, arrangements for vertical scanning of the electron beam,other than the preferred arrangement described herein, may be employedin conjunction with the horizontal scanning arrangement of the presentinvention.

Preferably, as shown in FIGS. 46, an electrically conductive coating 146of aluminum, aguadag, or other suitable material, is deposited orotherwise applied to the inside surface of the tube envelope 46 in thelower region 49 thereof and in the neck 51, in order to shield theseregions from undesired fields and deflection influences on the electronbeam 55 by external sources. This coating 146 also functions to maintainan equipotential region in the tube where the magnetic deflectionoccurs, so that more accurate magnetic control of the beam is achieved.Window openings 147 are provided in the coating 146 adjacent each of thehorizontal deflection pole pieces 58 and 59 to prevent induced currentlosses in the coating 146 that would be caused by the varying magneticfield produced by these pole pieces. A slit 148 is provided in thecoating 146 between and interconnecting the windows 147 to prevent therebeing closed electrically conductive loops around the peripheries of thewindows 147 which, if present, would permit circulating currents to beset up by the varying horizontal deflection magnetic field, whichcurrents would consume energy. No windows need be provided in thecoating 146 in the vicinity of the magnetic pole pieces 82 and 83because the magnetic field produced by these pole pieces is fixed ratherthan variable, and this fixed magnetic field does not produce currentsin the conductive coating 146.

The electron gun 54 and first-stage horizontal deflection pole pieces58, 59 are located so that the center of deflection of the horizontallydeflected electron beam is below and sideways from the target area 50,as shown at 181 in the figures of the drawing. That is, if the usefultarget area were projected downward or sideways, no part of it wouldpass over the deflection center 181 of the first magnetic field. Thus,the electron beam 55 always has a horizontal component of direction whenit enters the second stage magnetic field of uniform magnetic polarityproduced by the pole pieces 82 and 83, whereby the electron beam willalways be curved and rendered vertical by this magnetic field. Thisarrangement avoids picture distortion effects that would occur if thesecond stage magnetic field had a point of zero or reversing polaritythrough which the scanning electron beam must pass. Such a transitionpoint in the second stage magnetic field would cause distortions in thedeflection of the beam.

In describing and claiming the electron beam source and other componentsas being below the viewing screen or target area, it is to be understoodthat the term below is used for convenience as a reference direction andis meant to include equivalent positions or directions above or to aside of the viewing screen or target area.

After learning of the present invention, as described herein, oneskilled in the art may design various sizes and embodiments of cathoderay tubes in accordance with the principles of the invention, by variousmeans such as analytical or graphical design. For purposes ofillustration, a graphical design technique will now be described.

In FIG. 7, the numeral 181 indicates the compromise center of deflectionof the electron beam 55 as deflected by a magnetic field produced by thefirst deflection stage 56 of the horizontal deflection arrangement. Nowassume the electron beam to be directed from the center of deflection181, by the first deflection stage 56, at an angle oi with respect tothe vertical, at being variable as a function of time, so that at aparticular instant of time the central axis of the elecron beam followsalong a path 151. Now draw a vertical line 152 to indicate the path thecentral axis of the beam will follow after exiting from the seconddeflection stage. The position of this line is dictated by the selectionof time 1 within the horizontal interval. For example, if a linearrelation is desired between the angle of beam deflection caused by thefirst deflection stage and the horizontal scanning of the electron beambehind the screen 50, then 11 may be the midangle of the horizontaldeflection range caused by the first deflection stage, and the verticalline 152 will be midway between the left and right sides of the screen50. As a practical matter, this relationship preferably is chosen to benon-linear in a manner such that a readily obtainable wave shape ofhorizontal deflection signal will produce the required linear horizontalscanning of the beam behind the screen.

Assume a value of magnetic field strength or flux density for the seconddeflection stage which will cause the electron beam to curve on a radiusr of reasonable dimension for the size of the tube being designed. Forexample, a radiu r of 1.5 cm. has been found suitable for the cathoderay tube shown in the drawing. The value r is related to the magneticflux density by the formula where r radius of curvature of the electronbeam, in meters;

m=mass of an electron (9.ll kilograms);

e=electrical charge of an electron (1.602 10 conlombs);

V=potential of the electron beam, in volts, as determined by the lastelement of the electron gun (2,000 volts in a preferred embodiment); and

B magnetic flux density, in Webers per square meter, as produced betweenthe second deflection lens pole pieces by the magnet (0.01 Webers persquare meter in the embodiment shown in the drawing).

Then, draw a vertical line 153 to the left of, parallel to, and at adistance r from, the vertical electron beam path line 152. Draw a line154 above, parallel to, and at a distance r from, the electron beam pathline 151. About the intersection 155 of the lines 153 and 154, which isa center of deflection curvature, draw a circular are 156 connecting theelectron beam path lines 151 and 152. The are 156 shows the deflectionpath of the electron beam caused by the magnetic field of the seconddeflection stage. To determine precisely where the electron beam mustenter and leave this magnetic field, draw a line 157 from theintersection 155 normal to the line 151, and draw a line 158 from theintersection 155 normal to the line 152. The point 159 of intersectionof lines 157 and 151 is the point where the leading edge of thedeflecting magnetic field must be, and the point 160 of intersection oflines 158 and 152 is the point where the trailing edge of the deflectingmagnetic field must be, for the electron beam, when approaching thismagnetic field at an angle oi to the vertical, as shown, to exit fromthis magnetic field in the vertical path 152. The vertical distance v,shown by the line 161, is the vertical dimension of the deflectingmagnetic field between the beam entering and exiting points 159 and 160,and is defined by the formula v=r sin a where r is the radius of beamdeflection caused by the magnetic field and 0c is the angle of the beam,with respect to the vertical, as the beam leaves the first deflectionstage.

Now assume a slightly difierent angle of horizontal deflection of theelectron beam as caused by the first deflection stage 56, for examplecq-I-A, the increment A being such that the central axis 162 of thiselectron beam will approach the second deflection stage at a distancefrom the first beam axis 151 approximately equal to the width of anactual electron beam. Draw a vertical line 163 to indicate the path itis desired that the central axis of the beam will follow after exitingfrom the second deflection stage, as determined by t -I-At. Proceed, inthe manner described above, to draw lines parallel to the lines 162 and163, and at a distance r therefrom, to obtain a second center ofdeflection curvature which will be spaced from the previoisly foundcenter of curvature 155. Draw lines from this second center of curvaturenormal to the lines 162 and 163, respectively, to determine the points164 and 165 where the leading and trailing edges of the second stagemagnetic field must be to produce the desired beam deflection. Thelatter step are not shown, to avoid congestion in FIG. 7.

Next, draw a line 166 through points 159 and 164; this line 166 istangent to the leading edge of the deflection stage magnetic field atthe region where an electron beam at a deflection angle of A i-F5 willenter this second stage magnetic field. Draw a line 167 through thepoints 160 and 165; this line 167 is tangent to the trailing edge of thesecond deflection stage magnetic field at the region where the aforesaidelectron beam at the deflection angle of will leave this second stagemagnetic field. The lines 166 and 167 represent the practical edges ofthe magnetic field, neglecting the fringe field effects.

The next step is to compute, analytically, the exact shape of an actualelectron beam 171 as deflected at an angle by the first deflectionstage. FIG. 8 shows such a plot. Analytical methods of computingelectron beam shapes and trajectories are well known. In making thesecomputations, it should be observed that the actual center of deflection of the electron beam at the first deflection stage 56 will notnecessarily be the same as the compromise center of deflection 181. Theelectron beam 171 is a con verging electron beam, and has a cross-overpoint at 172 which is the point of minimum diameter of the beam alongits length. The best focus, i.e. the smallest spot size produced on thescreen 50 by the electron beam striking the screen 50, occurs when thebeam is at the cross-over point when it strikes the screen. For bestoverall focus of the electron beam on the screen, the locus of the crossover point of the horizontally deflected electron beam should lie on aline 173 extending approximately horizontally mid-way between the topand bottom of the screen 16. As shown in FIG. 8, the point 172 ofelectron beam focus is properly on the line 173. If, the first time theelectron beam focus is thus computed, the focus is not on line 173, itshould be made to fall on line 173 by varying one or more pertinentparameters, such as the original rate of convergence of the electronbeam, the location of the beam source, the location and shape of thefirst deflection stage 56, and the angle oc(l), of the beam produced bythe electron gun.

Similar computations are then made of points on the leading and trailingedges of the second deflection stage magnetic field, and the locus ofthe electron beam crossover points, for other values of deflection anglesuch as 04 and a +A etc., for the entire horizontal scanning range. Theexact order in which these computations are made is not critical. If itis found that the locus of best focus deviates unduly from the line 173,for example along a line 174, it will be apparent that the chosencombination of parameters will not produce acceptable focus of theelectron beam of the screen 50, and then one or more of the parametersmust be changed and the computations of the leading and trailing edgesof the second deflection stage magnetic field must be repeated. Thisprocedure is repeated until a suitable set of parameters is obtainedwhich will provide suitable overall size and shape; practical size,shape, orientation and magnetic strength of magnetic pole pieces forproducing the second deflection stage magnetic field (these pole pieceswill be slightly narrower than the magnetic field produced therebetween,due to well-known fringe effects which cause the magnetic field to bulgea bit beyond the edges of the pole pieces), a suitable linearlyrelationship of the deflected beam angle oc(l) with respect tohorizontal beam scansion behind the screen commensurate with a readilyobtainable wave shape of horizontal deflection signal, and suitablefocus of the electron beam at the screen.

Some electron beam deflection principles will now be described whichwill aid in choosing the parameters when making the aforesaidcomputations and graphic plots. First, referring to FIG. 9, it should berealized that, with the magnetic field tapered as produced by thetapered second deflection stage pole pieces in the preferred embodimentof the invention, i.e., tapered so as to become increasingly wider fromleft to right, so that the beam curves in a direction toward the morenarrow end of the magnetic field, this tapered magnetic field acts as aconvergent lens on the electron beam; i.e., it increases the beamconvergence and hence shortens the distance along the length of the beamat which the cross-over point occurs. This is readily seen from FIG. 9,in which 176 and 177 are mutually parallel leading and trailing edges ofa hypothetical second deflection stage magnetic field. Assume ahypothetical electron beam 178 having mutually parallel sides, i.e., abeam that is neither convergent nor divergent. The beam will be curvedby the magnetic field and exit therefrom at 179 with mutually parallelsides. Thus the magnetic field has not provided any lens action on theelectron beam. The reason for this is that the two curved paths 182, 183of the sides of the beam in the magnetic field, have equal lengths.

Now assume the second deflection stage magnetic field to have mutuallytapered leading and trailing edges 176' and 177', respectively. Theinner and outer sides of the electron beam are now curved differentamounts by the magnetic field, as shown at 182' and 183, the inner side182 being curved relatively less to exit on a path 184 and the outerside 183' being curved relatively more to exit on a path 185. As isreadily apparent, the tapered magnetic field has a convergent lensaction on the electron beam, so that the deflected beam converges to acrossover point at 186. Similarly, if the electron beam 178 is aconverging electron beam as in actuality, the convergent lens action ofthe magnetic field having mutually tapered leading and trailing edges176 and 177 will increase the beam convergence to give the beam ashorter focal length having a cross-over point at 187, for example.

From the foregoing, it is seen that the amount of convergence, and hencethe focal length of the electron beam to the cross-over point, can becontrolled or varied by choosing a proper taper, or rate of change oftaper, of the second deflection stage magnetic field. In the preferredembodiment of the invention shown in the drawing, the sides of thesecond deflection stage pole pieces, and hence the magnetic fieldproduced thereby, are so designed to shorten the focal length of theelectron beam more at the left than at the right, so as to move thecross-over point of best focus relatively down at the left and up at theright, this being in the proper direction to correct the undesiredslanted locus of best focus shown in FIG. 12. In the preferredembodiment, the taper of the second stage pole pieces has a point ofmaximum taper to the left of which the taper becomes relatively less.The reason for this is that the focal length of the system is determinedby the sum of the focus actions taking place in the first and seconddeflection means.

Another electron beam deflection principle used in designing anarrangement in accordance with the invention will now be described withreference to FIG. 10, and concerns the lengthening of the focal lengthof the deflection lens system at the right-hand region of the horizontaldeflection, in order to increase the distance along the electron beam atwhich the cross-over point occurs. Referring to FIG. 10, the convergingbeam 191 approaches the right-hand region of the second deflection stagemagnetic field 192 at a relatively acute angle 5. The electron beam hasa certain diameter or width 193 at the leading edge 194 of the magneticfield; however, the effective width of the beam coincident with theleading edge 194 is a larger value as shown at 196. Due to therelatively large curvature of the beam in this region of the magneticfield, the effectively larger entering beam width 196 causes the exitingbeam width to be greater, as indicated at 197, than the beam width wouldbe, as indicated at 198, if it were not for the combination of acuteentrance angle b and relatively large curvature of the beam in thisregion of the magnetic field 192. The vertically exiting electron beamwith its broadened base dimension 197, converges to a cross-over point199 which is higher than the cross-over point 200 the beam would havewith a non-widened base dimension 198. This effect of increasing thefocal length of the deflection system is greater than, and is slightlyreduced by, the tendency for the focal length to shorten slightly due toa slightly increased convergence caused by the slight mutual taperbetween the leading and trailing edges 194 and 201 at this region of themagnetic field.

From the foregoing, it is seen that the focal length of the deflectionsystem can be varied by proper combinations of angle of approach of theelectron beam to the second deflection stage magnetic field and theamount of deflection given the beam by this field.

The first deflection stage 56 affects the focal length of the electronbeam, by what is known as deflection focus. When the beam is deflectedby the first deflection stage 56, its convergence is increased, andhence its focal length shortened, as a function of the amount ofdeflection. Now referring to FIG. 8, the non-deflected beam, which isdirected in the direction 206, does not experience any deflection focus.When the beam is deflected to its most nearby vertical direction 207 bythe first stage 56, it has the relatively strongest deflection focus,thus shortening its focal length. This effect is desirable, because thefocal length of the beam must be shortened at the left-hand region ofhorizontal deflection in order to achieve good focus at the screen.Because of this, the second stage magnetic pole pieces need not betapered as much at the left-hand or narrower ends thereof as wouldotherwise be necessary. When the beam is deflected to its most nearlyhorizontal direction 208 by the first stage 56, it is given a moderateamount of deflection focus and less than when deflected to the direction207, because, in accordance with a feature of the invention, theelectron gun which produces the beam is tilted at an angle less than 45with respect to the horizontal. The deflection focus when the beam isdeflected to the direction 208, undesirably tends to shorten the focallength of the electron beam, which effect is overcome by the relativelygreater effect, as described above with reference to FIG. of increasingthe focal length due to the widening of the electron beam at 197.

The foregoing explanation and drawings graphically illustrate themechanisms functioning within the horizontal deflection system. Theactual design of the structure entails the application of analytictechniques. The general technique of designing different cathode raytubes in accordance with the invention is one of arriving at uniquegeometrical parameters of both electron gun orientation along withmagnetic fields that result in a linear, collimated, and optimumlyfocused electron beam projected vertically behind the screen. Theanalytic procedure consists of the following:

(1) Select an .approximate geometry of tube configuration and the firstdeflection means.

(2) Assume a practical drive waveshape for the dynamic magneticdeflection means (first deflection means). If a perfectly collimated andlinear horizontal sweep is required, there is one .and only one properlyshaped second deflection stage magnetic field which will fulfill therequirements.

(3) The second deflection stage magnetic field is now determinedanalytically by conventional ray tracing techniques and the focalcharacteristics of the entire system are likewise checked analytically.If the focal characteristics or the geometry of the system are notsatisfactory, one or more of the parameters in 1 or 2 will be changed.

(4) Continue iteration of above until optimum requirements are met.

The general structure arrived at through the above procedure, representsa unique and simple configuration which Will permit the construction ofa practical fiat display horizontal deflection system capable ofadequately fulfilling requirements of scan linearity and focus in suchdevices.

The desirability for improving the electron beam focus in flat cathoderay tubes, which is achieved in the present invention, will now bedescribed with reference to FIGS. 11 and 12 of the drawing.

FIG. 11 is a side sectional view of a typical widely used type of priorart cathode ray tube 213 and shows, in an exaggerated manner forillustrative purposes, the side-view shape of a typical electron beam216 produced by an electron gun 214. The beam 216, as it emerges fromthe gun 214, has sufficient cross-sectional area to provide adequateelectron-beam energy, and the beam is converging, i.e. the outer bundlesof electrons of the beam are converging, to a cross-over point 217 atwhich the electron beam has the smallest cross-sectional area and hencethe sharpest focus, and thereafter the electron beam 216 diverges asindicated at 218. As a practical matter, the cross-over point 217 willhave a finite cross-sectional area due to the effect of space charge ofthe electrons. In the well-known and widely used conventional type ofcathode ray tube 213 in which the electron beam is directedsubstantially perpendicular to the phosphor screen 219, the electron gun214 is designed to converge the beam 216 in such a manner that thecrossover point 217 will be approximately at the plane of the viewingscreen 219, whereby small spot size and hence good focus is readilyachieved over the entire area of the screen 219. However, in the typicalprior art fiat picture tube of FIG. 12 the convergence of the electronbeam must be chosen so that, as a matter of compromise, the best focuslies at the center 222 of the screen and only at certain other points onthe screen equidistant from the electron gun along the electron beampath, the focus being poor at other areas of the screen as will now bedescribed.

A typical prior art flat -cathode ray tube as shown in FIG. 12, lookingtoward the front thereof, consists of an evacuated envelope 226 providedwith a phosphor viewing screen 227 on the inside of the front wallthereof, the envelope 226 including a neck portion 228 in which anelectron gun 229 is positioned to provide an electron beam 231 in ahorizontal direction below and slightly behind the screen 227.Horizontal beam deflection means, not shown, which may consist of anarray of electrostatic deflection plates, is supplied with electricpotentials caus-' ing the beam 231 to curve upwardly at successiveintervals or locations so as to cause the beam 231 to scan horizontallybehind the viewing screen 227. For example, the left-most position ofthe horizontally scanned electron beam is indicated at 232; the centralposition is indicated at 233; and the right-most horizontally scannedposition is indicated at 234.

Vertical deflection means, not shown, and which may comprise an array ofelectrostatic deflection plates, is arranged behind the screen 227 todirect the electron beam 231 toward the screen 227 at successivevertical intervals. For example, if the electron beam when following thepath 232 is directed toward the screen 227 at the lower region of thescreen, the beam will impinge upon the screen at a point 236. If thebeam, when following the path 233, is caused by the vertical deflectionmeans to impinge centrally of the screen, it will thus impinge at thepoint 222; and if the vertical deflection means causes the beam, whenfollowing path 234, to bend toward the screen 227 near the upper portionthereof, the beam will impinge thereon at a point 223.

It will be evident that the electron beam path 323 is appreciablyshorter in length than the beam path 234. If the electron beam 231 is aconverging electron beam having a cross-over point, which is desirablebecause it provides adequate electron energy along with smallcross-sectional area at the cross-over point for achieving good focus,it is found that, unless dynamic focusing correction is employed in theelectron gun, uneven and poor focus of the beam occurs at the screen227. The best focus of the electron beam is at the cross-over point, andthe focus is increasingly poorer at increasing distances along theelectron beam from the cross-over point.

As illustrated in FIGS. 11 and 12, the cross-sectional size of theelectron beams 216 and 231 at points along the length thereofcorresponding to the points of impingement 236 and 223 on the viewingscreen 227 of FIG. 12, are considerably larger than that at the centralpoint 222, and intermediate points therebetween have intermediate sizesof cross-sectional area. In FIG. 12, the tilted dashed line 241indicates the locus of best focus of the converging electron beam on thescreen 227. The beam at point 222 and at other points along the line 241will have best focus; beam spots 242 and 243 generally will haveacceptable focus, and the beam spots 236 and 223 will have unacceptablefocus. It is known to employ a dynamic, i.e., a varying, focus techniqueat the electron gun or elsewhere to shift the cross-over point of theelectron beam while scanning over the screen in order to improve thefocus; however, this technique involves certain complications and thereare practical limitations to its effectiveness.

An important feature of the invention is the attainment of improvedfocus of the electron beam on the screen, as will now be particularlydescribed with reference to FIG. 13. The electron beam 55, as it leavesthe electron gun 54, is tapered in a converging manner with a degree ofconvergence to produce the cross-over point or best focus atapproximately the center 251 of the screen 50 when the beam is in itsundeflected or neutral position 73.

There is a smooth change in the focus action of the two magnetic fieldswhich causes decreasing convergence and hence a relative increase infocal length of the electron beam as the beam scans from left to right,so that the point of best focus lies along a line 252 extendingsubstantially horizontally across the center of the viewing screen 50.Since the locus of best focus extends substantially horizontally acrossthe center of the viewing screen 50, the locations of relatively poorestfocus will be at the top and bottom edges of the viewing screen 50, asindicated at the points 253-258; however, the focus or spot size atthese points will be of acceptable size. By comparing the electron beamspot sizes of the tube of the present invention as shown in FIG. 13 withthe spot sizes of the prior cathode ray tube shown in FIG. 12, it willbe seen that the spot size distribution of the present invention isconsiderably more uniform and the spot size is generally smaller. Thisimprovement in focus is obtained without the necessity of horizontaldynamic focus correction.

The above-described focus improvement applies to the dimension of thecross-section of theelectron beam 55 in the plane of the horizontal orline deflection, i.e. horizontally of the electron beam when it strikesthe viewing screen. The cross-over point of the electron beam is notaffected in the cross-section dimension normal to the plane ofhorizontal deflection; the focus in this cross-sectional dimension ofthe beam is controlled by the vertical deflection system. The horizontaland vertical focus effects combine to provide a desirable spot size andshape of the electron beam where it impinges on the viewing screen.

With the above-described preferred arrangement of the invention in whichthe neutral position of the electron beam is approximately centeredhorizontally of the screen 50 as indicated by the electron beam path 95,the horizontal deflection signal source 62 may be a conventionaltelevision deflection circuit producing a non-linear deflection signalas shown at 68 for successively deflecting the electron beam 55 to theleft and to the right of its neutral position, whereby the electron beamscans cyclically from left to right behind the viewing screen 50 in alinear manner with respect to time. If it is desired to use horizontaldeflection signals having a nonstandard wave shape, linear scanning ofthe electron beam behind the viewing screen can be achieved by acompensatory reshaping of the deflection pole pieces 58, 59. Since thefunction of the first stage 56 is to produce an angular deflection ofthe electron beam, any suitable equivalent deflection system, such aselectrostatic deflection plates, may be used instead of the magneticsystem shown, provided the deflection signal 68 has a suitable waveshape.

Although in the preferred embodiment of the invention, the electron gun54 is tilted at an angle of less than 45 degrees with respect to thehorizontal and is oriented so that the electron beam 55, when unaffectedby the first deflection stage 56, i.e., when the signal 68 has zerovalue, follows the paths 73 and 95 to pass upwardly behind the screen 50at approximately the center, if desired the electron gun may be tiltedat other angles if the deflection signal 68 is given a suitable waveshape or if a fixed amount of bias current is supplied to the winding 61to cause the beam 55 to have the desired neutral path 73-95.Alternatively, a permanent magnet may be employed to provide magneticbias.

Preferably, a high resistance material, such as chromic oxide, is coatedover the inside of the glass envelope 46 at the window openings 147 toprovide a leakage path from the window areas to the conductive coating146, to prevent stray electrical charges from developing on the envelopeat the window areas 147.

FIG. 14 shows, by way of example, a modified shape of the pole pieces82, 83 which results from designing the tube for use with a horizontaldeflection signal 68 of modified wave shape.

The new arrangements of this invention for producing and deflecting anelectron beam are found to be advantageous over prior art arrangementsin several respects. Good, and relatively uniform, focus is achievedover the entire area of the viewing screen. The magnetic beam scanningarrangement can function at relatively high repetition frequencies, suchas the horizontal scanning rate of television, without incurring theproblems of providing for fast discharging of deflection elements as isthe case with certain prior-art electrostatic deflection techniques. Thefirst and second horizontal deflection stages of the invention cooperateto provide a continuous'linear motion of the electron beam scanningbehind the target area, whereas certain prior art scanning arrangementstend to provide nonlinear or distorted scanning which results indistortion of the image reproduced on the picture tube. The inventionavoids the use of expensive and complex electrical commutatingarrangements which have been proposed in the past for causing deflectionof the electron beam in certain flat picture tubes. The required angleof deflection of the electron beam by the first-stage horizontaldeflection magnetic field, in the present invention, is easily achievedwith very low power, and generally is less than degrees. The preferredembodiments of the invention have further advantages in that the neutralor unscanned position of the electron beam is approximately centrallyaligned with respect to the viewing screen, without the need forapplying any bias voltages or fields to the horizontal scanning means,and thus the horizontal deflection may be achieved by the use of aconventional television horizontal deflection signal. The shape of thetube envelope minimizes the volume of air that must be evacuated,minimizes the spacing between the magnetic pole pieces which provide thefirst and second lens elements, thereby increasing the efliciency andpreciseness of the magnetic field lenses, and at the same time positionsthe screen forwardly of the electron beam source so as to permitaccurate vertical scanning of the electron beam on the screen.

In addition to achieving the aforesaid advantages, the flat cathode raytube of the present invention is capable of relatively inexpensive massproduction as compared with certain prior art types of flat picturetubes.

While preferred embodiments and modifications of the invention have beenshown and described, various other embodiments and modifications thereofwill be apparent to those skilled in the art and will fall within thescope of invention as defined in the following claims. It is to beunderstood that, although the present invention has been describedprimarily as useful for the horizontal scanning system in a flattelevision picture tube, it may also be useful for achieving verticalscanning, and furthermore is useful in cathode ray tubes other thantelevision picture tubes wherein it is desired to cause an electron beamto be scanned in the manner of the invention.

I claim:

1. A cathode ray tube comprising:

(a) an image target area having first and second orthogonal scandimensions lying in a first plane;

(b) means for producing an electron beam in a second plane spaced fromand generally parallel to said first plane and along an initial pathcanted with respect to said scan dimensions;

(c) first scanning means for cyclically scanning said beam within saidsecond plane along said first scan dimension, said first scanning meansincluding (1) dynamic deflection means disposed across said initialpath, with a center of deflection displaced from both said target areadimensions, for dynamically deflecting said beam along a plurality ofangularly spaced diverging paths, and

(2) static deflection means comprising means for producing asubstantially unidirectional magnetic field across said diverging pathsof said beam for statically deflecting said beam along a succession ofcollimated paths generally parallel to said second scan dimension andfor varying the focal length of said beam as it travels along differentones of said collimated paths such that the locus of the beam focalpoints lies along 1 5 a line generally parallel to said first scandimension; and

(d) second scanning means for cyclically scanning the beam along saidsecond scan dimension including dynamic deflection means disposed acrosssaid collimated paths for deflecting said beam from said second planetoward said target area.

2. The invention of claim 1, wherein the magnetic field produced by saidfield producing means has a leading edge and trailing edge disposedacross said diverging paths of said beam and inclined at an anglerelative to said first scan dimension.

3. The invention of claim 2, wherein the magnetic field produced by saidfield producing means includes a tapered end an a wider end with saidtapered end being located closer to said target area and said center ofdeflection than said wider end.

4. The invention of claim 3, wherein the magnetic field produced by saidfield producing means is tapered in accordance with the formula v:r sinoz wherein v is the distance measured along the direction parallel tosaid second scan dimension between the points at which a given electronbeam leaving said first deflection means intersects said leading andtrailing edges, r is the radius of deflection of said given beam causedby said field, and a is the angle of the path of said given beamrelative to said second scan dimension as it leaves said firstdeflection means.

5. The invention of claim 4, wherein: (a) said field producing meanscomprises a pair of opposing pole pieces disposed substantially parallelto said first plane and on opposite sides of said second plane, and

(b) said pole pieces having a leading edge and a trailing edgesubstantially coincident with said leading and trailing edges of saidmagnetic field.

6. The invention of claim 5, wherein:

(a) said first scan dimension is generally horizontal,

(b) said second scan dimension is generally vertical,

(c) said second plane is spaced behind said first plane,

(d) said beam producing means and said dynamic deflection means of saidfirst scanning means are displaced below and to the left of said targetarea, and

(c) said pole pieces are located below said target area with theirtapered and Wider ends respectively disposed below the left and rightedges of said target area.

References Cited UNITED STATES PATENTS 2,760,096 8/ 1956 Longini.

2,795,729 6/ 1957 Gabor.

2,850,669 9/1958 Geer.

2,872,607 2/1959 Gabor.

2,928,014 3/1960 Aiken et al.

2,999,957 9/1961 Schagen et al.

3,023,343 2/ 1962 Kuehler.

3,031,596 4/1962 Leboutet et al.

3,193,717 7/1965 Nunan.

ROBERT SEGAL, Primary Examiner US. Cl. X.R. 31379; 3l523

